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Gene targeting by the vitamin D response element binding protein reveals a role for vitamin D in osteoblast mTOR signaling

By Thomas S. Lisse, Ting Liu, Martin Irmler, Johannes Beckers, Hong Chen, John S. Adams and Martin Hewison

Abstract

Transcriptional regulation by hormonal 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] involves occupancy of vitamin D response elements (VDREs) by the VDRE binding protein (VDRE-BP) or 1,25(OH)2D3-bound vitamin D receptor (VDR). This relationship is disrupted by elevated VDRE-BP, causing a form of hereditary vitamin D-resistant rickets (HVDRR). DNA array analysis showed that of 114 genes regulated by 1,25(OH)2D3 in control cells, almost all (113) were rendered insensitive to the hormone in VDRE-BP-overexpressing HVDRR cells. Among these was the gene for DNA-damage-inducible transcript 4 (DDIT4), an inhibitor of mammalian target of rapamycin (mTOR) signaling. Chromatin immunoprecipitation PCR using 1,25(OH)2D3-treated osteoblasts confirmed that VDR and VDRE-BP compete for binding to the DDIT4 gene promoter. Expression of DDIT4 mRNA in these cells was induced (1.6–6 fold) by 1,25(OH)2D3 (10–100 nM), and Western blot and flow cytometry analysis showed that this response involved suppression of phosphorylated S6K1T389 (a downstream target of mTOR) similar to rapamycin treatment. siRNA knockdown of DDIT4 completely abrogated antiproliferative responses to 1,25(OH)2D3, whereas overexpression of VDRE-BP exerted a dominant-negative effect on transcription of 1,25(OH)2D3-target genes. DDIT4, an inhibitor of mTOR signaling, is a direct target for 1,25(OH)2D3 and VDRE-BP, and functions to suppress cell proliferation in response to vitamin D.—Lisse, T. S., Liu, T., Irmler, M., Beckers, J., Chen, H., Adams, J. S., Hewison, M. Gene targeting by the vitamin D response element binding protein reveals a role for vitamin D in osteoblast mTOR signaling

Topics: Research Communications
Publisher: Federation of American Societies for Experimental Biology
OAI identifier: oai:pubmedcentral.nih.gov:3042839
Provided by: PubMed Central
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